Can dogs sense the bond between humans?

My boyfriends dog is very protective and does not like people coming over to his apartment. But when I went over he acted as if he had already known me. This is the first time I was with the pup & he was very comfortable. He even cuddles with us. My boyfriend found it strange that he'd treat me like he treats him. I'm not fond of dogs and have never had one. His mom thinks its because my boyfriend and I have a very strong bond and are very alike.